Fuel cells are used as an electrical power source in many applications. In particular, fuel cells are proposed for use in automobiles to replace internal combustion engines. A commonly used fuel cell design uses a solid polymer electrolyte (“SPE”) membrane or proton exchange membrane (“PEM”), to provide ion transport between the anode and cathode.
In proton exchange membrane type fuel cells, hydrogen is supplied to the anode as fuel, and oxygen is supplied to the cathode as the oxidant. The oxygen can either be in pure form (O2) or air (a mixture of O2 and N2). PEM fuel cells typically have a membrane electrode assembly (“MEA”) in which a solid polymer membrane (i.e., ion conducting membrane) has an anode catalyst on one face, and a cathode catalyst on the opposite face. The anode and cathode layers of a typical PEM fuel cell are formed of porous conductive materials, such as woven graphite, graphitized sheets, or carbon paper to enable the fuel to disperse over the surface of the membrane facing the fuel supply electrode. Each electrode has finely divided catalyst particles (for example, platinum particles) supported on carbon particles to promote oxidation of hydrogen at the anode, and reduction of oxygen at the cathode. Protons flow from the anode through the ionically conductive polymer membrane to the cathode where they combine with oxygen to form water, which is discharged from the cell. The MEA is sandwiched between a pair of porous gas diffusion layers (“GDL”) which in turn are sandwiched between a pair of non-porous, electrically conductive flow field plates. The plates function as current collectors for the anode and the cathode, and contain appropriate channels and openings formed therein for distributing a liquid coolant and the fuel cell's gaseous reactants over the surface of respective anode and cathode catalysts. In order to produce electricity efficiently, the polymer electrolyte membrane of a PEM fuel cell must be thin, chemically stable, proton transmissive, non-electrically conductive and gas impermeable. In typical applications, fuel cells are provided in arrays of many individual fuel cell stacks in order to provide high levels of electrical power.
During fuel cell operation, water tends to accumulate at the bottom of the enclosure housing such fuel cell stacks (i.e., the wet end). Such water need to be removed so that the fuel cell stack can continue to operate properly. Some prior art solutions to this water accumulation use an active drain to remove water. Active drain systems are expensive and require a valve and water sensor to operate. Moreover, typically these systems only allow drainage at one location. However, automotive fuel cell systems need drainage at multiple locations in order to have efficient drainage when a vehicle is tilted. Other prior art drainage systems uses passive drain valve (e.g., umbrella, Bellville, duckbill) which require precise machining of the housing to function properly. Moreover, these passive drain valves require pressure head to open (up to 50 mm). This requirement can result in freeze issues.
Accordingly, there is a need for simple inexpensive systems for removing water from enclosures housing fuel cell stacks while still maintaining environmental sealing capability.